L [—1 WWII? HWWIWWW mescs 3 123 300860 6760 This is to certify that the thesis entitled ENEMYAMDQIRIITYSMJLATIOWW'HIEFMALPROCESSJNG IN CANS AND REIDRT POUCHES presented by JOHNMEGIAEL ORIGVSKI has been accepted towards fulfillment of the requirements for Master Of Science degree in Agricultural Engineering é; Major professor E; Datej/z/W 7? 0-7639 afi- LIBRARY § M." . 11".C‘“? Eviziilzgdar u. " OVERDUE PINES ARE 25¢ PER DAY PER ITEM Return to book drop to remove \a this checkout from your record. MSU mac 9 .s was '3 2 ,5; "i g ENERGY AND QUALITY SIMULATION OF THERMAL PROCESSING IN CANS AND RETORT POUCHES By John Michael Orlowski A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Agricultural Engineering 1979 ABSTRACT ENERGY AND QUALITY SIMULATION OF THERMAL PROCESSING IN CANS AND RETORT POUCHES BY John Michael Orlowski Computer models were used to simulate temperature changes, micro- bial destruction, and nutrient degradation occurring in pouches and cans during thermal processing. The optimum shape for a retort pouch was determined using a least cost approach based on nutrient retention and material requirements. The models were developed for conduction heated foods and use the sufficient lethal kill method as the criteria for determining sufficient process time. The 694.5 cm3 pouches with various shapes and equivalent lethal kill had process times between 40.4 and 49.6 minutes, and nutrient re- tentions (thiamdne) of 70.0 and 66.5 percent, respectively. A thinner profile pouch will have a shorter process time, with a much shorter cooling phase than a thicker pouch. The nutrient retention becomes lower and the processing time becomes longer as the container shape approaches a cube. The energy cost difference in processing equal volumes of food in pouches and cans is insignificant. The energy con- sumption is strongly influenced by the volume of material processed. Volumetric reduction, due to reduced liquid fill requirements, which may occur in pouch products can significantly reduce the energy re- quired for thermal processing. ACKNOWLEDGEMENTS The author would like to express his deep appreciation to Dr. James F. Steffe, for his guidance, support, and patience. Dr. R. C. Nicholas, Dr. C. A. Rotz, and Dr. D. R. Heldman are acknowledged for their assistance. The author would also like to express his gratefulness to the members of Room 6, for their encouragement. ii TABLE OF CONTENTS Page List of Tables v List of Figures vi nomenclature viii Definition I 1 ix Chapter I Introduction 1 1.1 General Remarks ‘ ' 1 1.2 Objectives 2 II Literature Review 3 2.1 Pouch Construction and Characteristics 3 2.2 Advantages of the Pouch 4 2.3 Disadvantages of the Pouch 9 2.4 Methods of Measuring the Slowest Heating Point .7 14 2.5 Conduction Heated Foods 14 III Theoretical Development 16 3.1 General Rate Equation 16 3.2 Rectangular Heat Transfer Model for Pouches 17 3.3 Cylindrical Heat Transfer Model for Cans 19 3.4 Thermal Diffusivity of the Food Models 22 IV Methods 23 4.1 Can and Pouch Simulation.Models 23 iii VII 1v 4.2 Description of Pouch Model 4 .3 Model Adoption and Verification 4.4 Comparison of the Can and Pouch Models ~ Results 5.1 Rectangular Model Results 5.2 Comparison of Square and Rectangular Pouches 5.3 Can Simulation Results 5.4 Comparison Between the Pouch and Can Simflation Studies 5.5 Small Pouches Compared With the 4.37 cm Radius and 11.57 cm Height Can . Conclusion Appendix A Computer Program to Simulate the Thermal Processing Of A Pouch Type Product Appendix 3 Computer Program To Simulate The Thermal Processing Of A Canned Product Appendix C Computer Results of Selected Computer Outputs Appendix D Energy Cost Equations List of References General Bibliography 24. . 30 33 38 38 38 42 42 51 56 58 61 64 70 72 7S LIST OF TABLES Table ‘ 2.1 The energy requirement for manufacturing container mater— ial for various types of containers (Schulz, 1978) 2.2 Improved processing times reported for retort pouches. 2.3 Equipment speeds for vacuum.and sealing machine used with retort pouches. 4.1 The validation of rectangular model comparing the original model to the revised model. 4.2 The validation of cylindrical model comparing Problem 2 in Teixeira et.a1. (1969) and the revised model. 4.3 Comparison between models using extreme container sizes and a constant volume of 694.5 cm3. 4.4 Dimensions of the containers simulated by the retort pouch processing model. 4.5 Dimensions of the container simulated by the can proces— sing model. 5.1 Results of simulating the thermal processing of conduction heating food contained in pouches. 5.2 The results of simulating the thermal processing of con- duction heating food contained in cans. 5.3 Energy and cost comparison calculated by simulating the thermal processing of pouches of various sizes. 5.4 Energy and cost comparison calculated by simulating the thermal processing of various can sizes. 5.5 Energy and cost comparison calculated by simulating the thermal processing of small pouches of various sizes. 5.6 The optimum container size for pouches and cans based on material cost and percent thiamine retention. 10 32 32 35 36 37 41 43 49 50 52 55 LIST OF PIGURES Figure 3.1 Labeling of nodes for finite cylinder used in the heat transfer simulation model. 4.1 Labeling of nodes for a rectangular parallelpiped' for use in the computer simulation.model. 4.2 A view of a central cube with surrounding locations. 5.1 Variation in heating time with thiCkness for a conduction heating food in square and rectangular pouches. 5.2 Variation in the percent retention of thiamine with thick- ness for a conduction heating food in square and rec- tangular pouches. 5.3 The variation in heating time (total time with steam on) with changes in the radius. 5.4 The variation in percent retention of thiamine with changes in can radius. 5.5 Retort temperature and center temperatures of a can and pouch of equal volume as a function of process time. 5.6 Retort temperature and center temperature of a can and pouch of unequal volume as a function of process time. 26 27 39 40 44 45 48 53 NOMENCLATURE AD, BO, CO . length, width, height of rectangular containers (cm) C - concentration of spores per cm3 Co - initial concentration of bacteria a time - 0 (spores per cm3) D - decimal reduction time, the time at a specified temperature (DN) necessary to destroy 902 of the organisms present in a given container (minutes) DN - time to destroy 902 of a vulnerable factors: temperature TN DTR - decimal reduction time at reference temperature TR (minutes) f - time for the straight line portion of heating Curve to transverse one log cycle (minutes) F8 value - the number of decimal reductions of the process h - half height of cylindrical container (cm) (1,3) - spatial nodes in the cylindrical coordinate system k - constant 0m,n,k) - node location for Cartesian geometry used in rectangular model NA, NB, NC - number of increments for rectangular container r radial distance from centerline (cm) t time (minutes) T - temperature (°C) T(i,j) - temperature at the node location (i,j) refers to cylindrical geometry T(m,n,k) - temperature at the node location (m,n,k), refers to Cartesian geometry Tc - temperature at the geometric center (°C) TN - temperature corresponding to DTR (°C) I; - temperature at the surface (°C) TR - reference temperature (°C) T‘ - steam temperature in retort (°C) vii x, y, z - the Cartesian Coordinate axes y - height from.mid-plane (cm) for the cylindrical geometry 2 - reciprocal of the slope of a Thermal Death curve of an organism.(C°) ZN - thermal destruction constant for vulnerable factor (C‘) a - thermal diffusivity (cmzlx) Ah spatial increment in the h direction (cm) Ar - spatial increment in the r direction (cm) At - time increment.(minutes) Ax - spatial increment in the x direction (cm) Ay - spatial increment in the y direction (cm) Az - spatial increment in the z direction (cm) viii I INTRODUCTION 1.1 General Remarks The Federal Government and private industry are interested in the energy savings which may be achieved by processing food in a retort pouch as opposed to the traditional can. Food items need a certain de- gree of heating before they may be considered a commercially sterilized, "safe" product. The geometry of the retort pouch is favorable to heat transfer allowing reduced (compared to the can) energy inputs during processing. Other advantages of the retort pouch over the can include the following: 1. Less energy is requiredéto manufacture the packaging material. 2. Packaging material is lighter in weight. 3. Geometry allows improved utilization of storage space. 4. Size and weight reduce transportation cost ($/ unit volume). 5. Reduction in overcooking (overheating) resulting in improved nutrient retention. 1.2 Objectives This research was an analytical study with the following objectives: 1. To provide a literature review of the "state of the art" in retort pouch technology. 2. To conduct simulation studies to compare the energy cost and nutrient retention of conduction heating foods in various size pouches and cans of equal volume. 3. To compare the energy cost and nutrient retention of various size pouches and cans with different fill volume and equal drained weight. 4. To recommend an optimum.pouch size based on nutrient content and a cost analysis. II LITERATURE REVIEW 2.1 Pouch Construction and Characteristics The retortable pouch is a lightweight, three—ply (polyolefin, polyester, and aluminum) container that will maintain integrity with temperatures above 121° C. The result of this material combination is a container that is impermeable to light, water vapor, and microorgan- isms. Each of the layers provides vital functions necessary for the integrity of the pouch. Polyolefin, the inner layer, is responsible for allowing the pouch to be heat sealed and it protects the aluminum layer from-internal damage. The middle layer is aluminum which provides both a vapor and light barrier. Using aluminim is essential for main? taining a shelf life of over two years for most retort pouch products. Pelyester film, the outer layer of the retortable pouch, protects the aluminum film.from external mechanical damage and provides a surface suitable for printing. A.vacuum.is created inside the retort pouch before it is fused closed. Vacuum packaging and heat sealing are important aspects of the pouch processing. The vacuum causes the pouch to conform to the product geometry. This allows for improved heat penetration and gives the soft pouch material a semi-rigid shape.' The fused seal also predludes all movement of material in or out of the pouch (Wilson, 1978). The food industry has been inundated with articles in journals andmagazines proclaiming the advantages of the retortable pouch. Usually, the articles carry little technical information and often cite the 3 4 billion.dollar prepared food industry as the market potential. Most of the recent literature has appeared in trade journals as general informa- tion or advertising. The claims, which will be dealt with individually in the following paragraphs, are greatly improved product quality, light‘ weight package material, reduced processing time, better use of storage space, and interference by the Food and Drug Administration (FDA) and United States Department of Agriculture (USDA). Most of the initial work on the retort pouch techonology was sup- ported by the United States Army. When the technology proved feasible the Army decided to covert all field rations to retort pouch containers. Subsequently, the food industry began to work on obtaining part of the guaranteed multi-million dollar market. With the influx of people came new ideas such as the retort tray and retortable cup (Banner, 1979). The standing pouch was also introduced. When this three-ply pouch is filled the bottom expands and may be used to support the pouch in an upright position. When empty, the standing pouch will require the same space as a regular pouch. The lower section of the pouch contains ad- ditional folds which allows the base to expand. This is a problem area because the folds and seams cause stress points that may lead to pin- holes (small cracks in the aluminum layer which allow oxygen to enter the package). 2.2 Advantages of the Pouch One advantage of the institutional pouch versus the number ten can (3.03 liters) is lower cost. The current (1979) price of a number ten can is 42c and the cost for the corresponding pouch is 21¢. The processor may be able to further reduce cost by using a smaller capacity pouch because pouch type products may require less brine or other liquid fill than do can products. Retort pouch material offers significant energy savings when come pared to other food containers. Manufacturing of the retort pouch requires less energy than that needed to make frozen food packages, glass containers, and tin-cans. Table 2.1 shows the energy requirements for manufacturing other containers (Schulz, 1978). The pouch currently costs less than the other containers. As energy prices continue to rise, the cost of a pouch will be increasing at a slower rate relative to the cost of the other containers. Another form of energy savings obtained by using a retort pouch is reduced processing requirements. The products packaged in pouches have a shorter cooking time than similar products packed in glass jars or tin-cans. The length of the processing time is dependant on the thickness of the pouch. A thinner profile will require less processing time because of the improved heat transfer to the slowest heating point. The improved processing times are quoted on Table 2.2. The energy required to thermally process fro- zen food is less than that required for a pouch. However, the refriger- ation requirements during storage cause frozen foods to be very energy intensive. Overall, it has been reported that pouched food requires sixty percent less energy than frozen food (Lustucru's, 1979). Due to the lightweight nature of the constituent materials, the pouch has an advantage over glass or tin. The retort pouch will weigh ten percent of a can and five percent of a glass container when empty (Lustrucru's, 1979). A full pouch with an equal quantity of food will weigh fortybfive percent less than a full can (Rubinste, 1964). This weight reduction is based on foods with a large amount of fill water. Part of the weight savings is from using lighter container material, the other portion is reduced fluid in the pouch. A full pouch will contain about ten percent water while forty percent of the total can weight is water (Abbott, 1977). The reduced weight (302) will save at least ten percent of the freight cost (Goldfarb, 1971). Either empty or full, the retort pouches have less void space than stacks of cans or glass jars. Full pouches require twenty—five percent less space than cans (Rubinste, 1964). Pouches also require less space when empty. A 13.7 meter long tailer will hold under 200,000 227-gram empty cans. The same trailer would hold 2.3 million empty preformed pouches (Abbott, 1977). The combined effect of reduced warehouse space for empty and full pouches is partly offset by the fact that full pouches cannot be stacked as high as cans. The 0.3. Army has . "Meal-Ready to Eat" (MRE) program. The um: program. takes full advantage of the pouch which is well suited for indi- vidual servings, portion control, and product variety. The army has developed a menu with at least seventeen different meat, vegetable, and dessert items (Davis, 1972). Portion controlled, individual serving pouches are placed into separate cardboard cartons and shipped in larger boxes. It is possible for military personnel to carry an entire meal in the pocket of a field jacket. The retort pouch can be fitted to the food producers needs. Pouches can be made from roll stock or purchased as preformed containers. The advantage of the preformed pouch is that the food processor only needs to seal one edge of the container. The advantage of roll stock is the flex- ibility concerning pouch size. However, better quality control is re- quired due to the problems caused by the necessity of sealing all four sides of the pouch. Table 2.1 The energy requirement for manufacturing container material for various types of containers (Schulz, 1978). Container Type Retort Pouch Frozen Food Glass Jar Tin Can Joules/container*** 2.04 x 105 2.97 x 105 3.35 x 106 3.76 x 106 *** 227 grams (8 ounce) food container, material and label Table 2.2 Improved processing time reported for retort pouches. Rubinste, 1964 Abbott, 1977 Pereira, 1978 502 less than cans 402 less than cans 30-502 less than cans 8 Products processed in a pouch will have improved quality. The thin profile of the pouch reduces the cooking time required to obtain a commer- cially sterile product. Correspondingly, the shorter process time allows for better nutrient retention. Some nutrients are heat sensitive and easily degraded when processed for long periods of time. The geometry of the can causes much of the product to be over-cooked. This excess cooking destroys valuable nutrients. Over-cooking will cause needless cell damage to vegetables and meats which further reduces the quality. Periera (1978) showed improved firmness, color, and texture when using the pouch to process green beans as compared to cans. Another means of assuring product quality is to flush and vacuum pack the product. The flush and vacuum process is difficult for can processing and ideal for pouches. ‘The pouch has a fused seal which inhibits oxygen transfer, and the soft nature of the pouch allows the vacuum to conform the pouch to the product geometry. This process will remove most free oxygen from the pouch which may chemically react with the product. This reaction may reduce the product quality by influencing the color, nutrient content, and texture. The tin-can does not have the positive seal of the pouch. A tin-can has a large headspace, and more free oxygen to reduce the product quality. The improved quality of the pouch products has been demonstrated in a preference test involving the free choice of meals (Schultz, 1978). A hydrostatic cooker, commonly used with tin-cans, is suitable for retort pouch processing. The closing equipment utilized seals the pouch in the final stages of sterilization (Wilson, 1970). During processing, individual pouches are conveyed upright through the retort. The conveyor holds the pouches in such a manner than a one way valve is formed at the seal. The valve allows gases to leave the pouch and nothing is permitted 9 to enter. This significantly reduces the free oxygen in the pouch headv space (Wilson, 1970). The normal closing operation involves vacuuming and sealing the pouch. In the hydrostatic process, the high temperatures drive all the free gases out of the product and only sealing remains. Eliminating the vacuum step allows more time for sealing which results in stronger seals (Wilson, 1970). 2.3 Disadvantages of the Pouch The retort pouch is not the final answer to the food industries problems. The most significant factor against the pouch, compared to the can, is the slow vacuum and sealing machine speeds. There are several reasons for the slow equipment. 1. The industry is young and capital has not been available for machine development. 2. The army spent important lead time and money on the development of pouch materials instead of pouch processing equipment. 3. The soft nature of the pouch requires special handling. 4. The pouch is not as easy to convey as a can. In order to compete with cans the line speed would need to be at least 400 pouches per minute, (Lemaire, 1978). It appears that the second generation of pouch filling and closing machines will have about half the speed needed.to compete with cans (Table 2.3). The equipment cost is an important factor. A machine capable of closing 15 pouches per minute would cost $100,000 (Lemaire, 1978). To produce 100 pouches per minute would require a $1 million investment (Lemaire, 1978). Pinto (1978) suggested buying several low capacity durable machines rather than risking a high capacity unproven model. :10. Table 2.3 Equipment speeds for vacuum and sealing machines used with retort pouches. Sggggg - Pouches/Minute Pinto, (1978) 10-15, 30-60 Lustrucru's, (1979) 25 Banner, (1979) 20-30 large pouches Europe's (1979) 100 User, (1979) 50—60 (mid-1979) . 250 (late-1979) 11 Labor is one of the more expensive inputs into the pouch processing system. Many meat items and institutional size pouches require hand fill- ing. A commercial hand fill operation averaging four pouches per minute has been reported (Pinto, 1978). At this slow speed labor becomes a crit— ical problem. Labor is required for several operations such as loading and unloading the racks which hold the pouches during retort processing. The total labor requirement in a production operation (pouch sealing to .case loading) for 120 pouches per minute is 14 to 16 people (Lemaire, 1978). Another problem with using the pouch has been government regulation. The Federal Government was initially concerned with the leaching of the bonding material into the food (Abbott, 1977). This problem has been solved by using the three-ply pouch material so "no adhesive" is used to seal the pouch. The inner lining of the pouch provides the heat sealing surface. After the material was approved, the United States Department of Agriculture (USDA) limited the amount of meat which could be processed in a pouch to 0.45 kg (about one pound). Andres (1979), who discussed this problem does not quote the USDA reasoning in the matter. The weight limit causes two problems. First, the family unit would have to buy sev- eral pouches of one item for a main dish. Secondly, the institutional market will have no number ten can equivalent pouches for meat products. The Food and Drug Administration has set no limdts on pouch capacity. However, pouches must be placed in a carton for protection. Even with the additional cost of the carton, the total cost of the pouch product is less than that required for a comparable can and label (Andres, 1979). One area of difficulty has been in obtaining high quality materials which could be used to make pouches. In the early 1970's a roll of pouch 12 material frequently was not cut squarely and the variation in the width caused machinery problems related to pouch formation. There were also problems in obtaining pouch materials during 1974. The industry was very small and the raw plastic was not available during the oil embargo. As a result, hasty substitutions were made for the normal pouch.materials. In one case, a degradable package was formulated and sold. Needless to say, there were difficulties (Donley, 1979). Even today, there is‘a limited number of suppliers and there are no industry standards used to judge the quality of pouch materials (Donley, 1979). Manufacturers estimate that 95 percent of the retortable film.produced is good (Pinto, 1978). The strength of the pouch seals have been tested by various methods. However, there are no industry standards as to the minimum strength. The U.S. Army ran numerous tests on the retortable pouches before they decided to adopt them in the "Meals Ready to Eat" program. Lampi et.a1. (1976) gives a clear description of each test and the related standards. In summary: 1. Fusion test is a visual examination of the seal and weld of the inner lining. Z. Burst test determines the pressure required to break the pouch seal. 3. Visual examination grades the severity of lines, air pockets, and food materials in the area of the seal. 4. Infrared scanning measures differences in the seal thickness. 5. Caliper measurement determines variation in thickness not visible to the eye. Although these tests are not industry standards, they could serve as val- uable guides for the future. 13 Another problem related to the commercial development of the pouch products is the lack of marketing information. International Telephone and Telegraph Continuum test-marketed a line of pouch products in 1977 but was forced to cancel the program due to an inability to keep up with consumer demand (Lemaire, 1978). ITT-Continential is expected to resume testing in mid-1979 (Banner, 1979). This is the first company to market the pouch on a large retail level to consumers. In contrast, Hormel Inc. has been operating in the speciality market for several years. The spec- iality market consists of government programs and special camping suppliers. Hormel offers eleven meat based products. Although the response has been favorable in the speciality market, the cost of $1.05 - 1.10 for 0.085 to 0.113 kg of product will not compete well in the general consumer market (Banner, 1979). In addition the consumer needs to be educated in the uses and advantages of the pouch. The distribution system must also adapt to the flexible pouch and carton. The flexible nature of the pouch requires special handling during processing. Pouches cannot be placed directly into the retort because unrestrained pouches will fold, bend, and swell thus inhibiting uniform heat transfer. For this reason, retort pouches must be placed in a hold- ing or restraining device. Small pouches can be placed in vertical racks, (Pflug -et.al. 1965; Davis et.al. 1972) which enhances both heat pene- tration and heating medium circulation. Institutional pouches have an additional problem because of their large mass.. The high weight places additional stress on the seams which may result in pin-holes. This problem is avoided by placing the large pouches on uniformly spaced horizontal racks. An overriding pressure is required for processing both large and small pouches to keep the pouch from excessive expansion during the heat- ing process. 14 2.4 Methods of Measuring the Slowest Heating Point The flexible nature of the pouch causes difficulty in measuring the slowest heating point. As the pouch expands during processing the slowest heating point may actually move. Three methods of inserting and holding the thermocouples in a pouch are available.‘ The methods are gland (Davis et.all. 1972; Pflug et.all. 1963), gussed and lead CPflug et.a1.. 1963). The gland method is most commonly used today. This method does not involve sealing the pouch around the thermocouple wires. Before filling the pouch a gland is attached to the pouch wall and the thermocouple wires are inserted through the gland into the pouch. 2.5 Conduction Heated Foods Various methods for describing heat transfer in conduction heated canned foods have been well documented. Several computer simulation models are available for solving conduction heating problems in cylindrical con- tainers (Hayakawa et.a1.. 1968; Manson et.a1.. 1967; Teixeira, 1978; Teixeira et.al. 1969). Herndon et.al. (1968; 1969; 1971) used computer derived tables to solve conduction heating problems in cans. Lenz and Lund (1977) describe the lethality-Fourier number approach to solving conduction heating problems in finite cylinders. Board and Steel (1978) used an "automated version" of Gillespy's method of solving heating problems. There are several books available which describe one or more methods in detail (Ball, et.al. 1957; Stumbo, 1965). There is a limited amoung of published material on non—cylindrical conduction heated foods. Two of the most recent reports are given by Manson et.al. (1970, 1974). The first study deals with rectangular containers and the second study deals with pear-shaped (hsmeshaped) containers. Both of these papers use a computer simulation approach to analize the problem. 15 The rectangular model can be applied to retort pouch processing and is discussed in greater depth later. III THEORETICAL DEVELOPMENT 3.1 General Rate Equation The general rate equation has been shown to be an affective analytical tool for describing the destruction of microorganisms. This equation has been useful in the analytical determination of "commercial sterility." Heat degradation of several quality factors can also be described as first- order rate processes. The general rate equation (at a constant tempera- ture) may be described, in terms of bacterial concentration, as dC/dt e -kc [l] where C - concentration of bacteria (spores per cm3) k - constant t - time (minutes) Integrating equation [1] and converting to common logarithms yield C . Co 10{-2.303 x t/D) [2] where Co - initial concentration of bacterial at time - 0 (spores per cm3). The decimal reduction time is temperature dependant and specified by D - decimal reduction time, the time at a specified temperature necessary to destroy 90 percent of a given organism (minutes) (Note D - 2.303/k) dD/dT - -D/Z [3] where T - temperature (°C) 16 17 z - thermal death constant for a particular organism (°C) Integrating equation [3] and converting to common logarithmic yields (TR—T) n - m 102'303 z [a] where DTR - decimal reduction at reference temperature TR (°C) TR - reference temperature (°C) Substituting equation [4] into equation [2] to give C in terms of temp- erature gives 2.303(TR-T)/Z) c _ Co 10(«2.303t/(D‘rlit 10 ,) [5] Equation [5] determines the concentration of bacteria. after holding at a specific temperature (TR) for time (t) when the initial concentration was Co. Equation [5] may also be used to describe vitamin destruction and 7 is best suited for small volumes with uniform temperature. To account for transient temperatures it is necessary to incorporate the differential equations of heat transfer. Heat transfer models for the can and pouch will be developed in the next two sections. 3.2 Rectangular Heat Transfer Model for Pouches In order to simulate the pouch shape it is necessary to develop a rectangular heat transfer model. This model will predict the temperature at locations throughout the pouch. The pouch model uses the Fourier equa- tion for 3—dimensional,transient, isotropic heat conduction, written as' aware”; .13. [6] 33:2 M2 322 at where (x,y,z) are the three planes in a Cartesian Coordinate system a _- thermal diffusivity (cmz/sec) 18 Using a finite difference method with the central difference formula (Ksrleker et. a1., 1977), the differentials given in equation [6] may be rewritten as .1233. - (11m + at); — 2T(m.n.k) t um - 1.n.k)) 3:2 A12 [7] 3.3!. - (TQM! f 133):- ZTTCMLKI-twin-1433 [81 3Y2 Ay 2 3:2. . (TQM.n.k'+ 1) - 2T(m,n.k) + Tszn.k ' 1)) [9] 3'2 2 AZ 2 3T ' a: T(m,n,k) (t + At) - T(m,n9k)t [10] where (m,n,k) are node points in the Cartesian Coordinate system A Taylor series expansion is necessary to derive equations [7-9]. Using this technique an error of the order of [(x)2/12] is generated (Karleker, et. a1. 1977). This error is negligible if small spatial and time in- crements are used in computation. Substituting equations [7-10] into equations [6] yields T(m+l,n,k) - 2_T4(m,n,k) + T(m-1,n,k) + T(m,n+1,k) - 2T(m,m,k) + T(an-1,k) sz AyZ + T_(m,n,k+l) - 2T(m,n,k) + T(m,n,k-1) - T(mJn,k) (t+At) —- T(m,n,k)t [11] Az2 a The boundary and initial conditions for cooking a pouch product are uni- form initial temperature (equations [12-14]),=r'surface temperature equal to retort temperature with time greater than zero (equation [15]) and cen- ter temperature reaches retort temperature as time approaches infinity (equation [16]). 3.2 3x - 0 at t - 0 [‘12] 19 ~33 - 0 at t - o [12] an: §«_’1_‘ - 0 at t - 0 [13] iy' 3T 5 0 at t 0 [14] T8 - Ton at the surface, when t.'<0 [15] T8 is the surface temperature (°C) Tan is the steam temperature in retort (°C) Tc - Ton at the center when t >>’0 [16] Tc - temperature at the geometric center (°C) The heat transfer model required in the computer simulation of retort pouch thermal processing is based on equations [11 d 16]. 3.3 Cylindrical Heat Transfer Model for Cans This can model is a transient, cylindrical conduction heating model with isotropic material and uniform initial temperature. The general dif- ferential equation for a finite cylinder is azr+ial+azr - m2 rar ay2 .1. ii a at [17] where r - radial distance from centerline (cm) y - vertical distance from.mid-p1sne (cm) Figure 3.1 describes the location of r and y with respect to the center of the container. Using a finite difference method with the central difference formulas the differentials of equation [17] may be rewritten 88 20 2.3!. . guy-1L1) - gum) + Riv-123)) [18] 31-2 ' Arz 123: . (Tail-+1.) - 2111.11 + TEL-1‘1” [19] ayz A72 2.! ’- TCH'I: ) "’ Tgf‘laj) 3]." 2A]? [20] 3% T(i.3)(t+At) - T(1.j)t [21] where i and 1 refer to spatial nodes in the cylindrical coordinate system. Substituting equations [18-21] into equation [17] results in (1041.1) '- ZTLi-ii) 4' Mir-1.1)) + T(1+1;J) - Iii-1,1) + Arz 2rAr trawl) - 2m,» + run-1) - (1(1a)(‘+m - mm") Ay2 a [22] At the centerline (r equals zero) and equation [22] is not valid because the second term is undefined. However, the (l/r)(3T/3 r) term can be determined by taking the limits as r goes to zero. Using i 'Hopital's rule (Thomas, 1969), the (l/r)(3T/3 r) term is written as w [H lim r+0 0: I1 I [23] "I The second term in equation [22] can be substituted by equation [18] to describe the temperature at the centerline. This substitution yields 2(T(i+l,j) - 21.6111) 4' TCi-IL‘D) + T(i,i+l) + -2T(i,_‘]) + TCilj-l) 41:2 Ayz +A -- (1/a) [241 The boundary and initial conditions for the can model are uniform initial temperature (equations [25] and [26]), surface temperature equal to retort temperature with time greater than zero (equations [27] and [28]), and 21 It: - PLANE / glut: CFNTfR 4L_- FIGURE 3.1 Labeling of nodes for finite cylinder used in the heat transfer simulation model. 22 center temperature reaches retort temperature as time approaches infinity (equation [29]). 31B 5;. 0 t I 0 [25] 3T '5'; 0 t 0 [26] Ta - T“, r - R, t > 0 ‘ I27] T8 ' T”, y . Y, t > 0 [28] T8 - T”, r - 0, t >> 0 [29] The heat transfer model required.in the computer simulation of the thermal processing of canned products is based on equations ['22. 24 and 25-29.] 3.4 Thermal Diffusivity of the Food Models The value of the thermal diffusivity of a -food material is required to determine the temperature gradient within the product. For the pouch model the thermal diffusivity is based on the Heisler charts and the cor- responding solutions for temperatures in a rectangular parallelepiped. The result is o - o.933/4((1/A0)2+(1/30)2+(1/c0)2) fh [30] where A0,BO,C0 are the lengths of the three sides of the parallelepiped. fh is the reciprocal of the slope of the straightline portion of the center point heating curve. fh is based on the food prop- erties (the value used is typical of those found for most foods). The can model is based on a finite cylinder and the corresponding thermal diffusivity is u - 0.398/((l/r)2 + (man/112)):h [31] where ‘ h e the half height of the container IV‘METHODS 4.1 Can and Pouch Simulation Models The retortable pouch model is based on a rectangular heat transfer model and the general rate equation to describe bacteria destruction and thiamine degradation. Equations [5,11-16] were programed by Manson et.al. (1970) and his computer model was adopted for use in this study. The can model is based on a cylindrical heat transfer model and the general rate equation in describing bacteria destruction and thiamine degradation. Equations [5,22,24,25-29] which compose the can model were programed by Teixeira et.al. (1969) and that computer model was also adopted for use in this study. The pouch and can models will allow for the simulation of a wide range of container sizes. The rectangular model simulated the retort pouch and involved thickness between 1.32 cm and 8.86 cm. Two volumetric capacities were considered in this study: 694.5 cm3 and 70 percent of 694.5 cm3 or 486.2 cma . This variation in volume is based on the reduced fill water required in pouches as compared 'with cans (Abbott, 1977). The 694.5 cm3 volume is representative of medium can sizes and was calculated from the nominal dimensions of a N0. 2 can (307 x 409). The variation in pouch dimensions allowed for a comparison of the amount of container material required, food quality, process time, and energy utilization. The dimensional changes are also useful in validating the models. The cylindrical model was used to simulate various can shapes of equal volume (694.5 cm3). The simulation studies of can shapes allowed 23 24 the comparisons mentioned for the pouch to be made for the can. The pur— pose in simulating the thermal processing of pouches and cans was to come pare the results and to make recommendations as to optimum container size. The can and pouch simulatioanodels-u e the same basic assumptions and parameters. The pouch model will be described in detail so the functional characteristics of both models may be clearly understood. There were a number of temperature assumptions made in developing the computer simu- 1ation models. The assumptions may be summarized as follows: 1. Initial product temperature is 76.7° C (170° F). 2. Retort temperatures during cooking is maintained at 121° C (250° F). 3. Product is cooked in water maintained at 26° C (79° F). 4. Cooling is complete when the product center temperature equals 76.7° F (170° F). 4.2 Description of Pouch Model A rectangular container is easily described in terms of its height, width, and thickness. Using the Cartesian Coordinate system, a grid is formed (Figure 4.1). Each grid location has a unique descriptor or variable name (i.e., (1,1,1,) or (2,4,1)). By symmetry, the bottom and top, the right and left side, and the front and back are all mirror images. Therefore, it is possible to generate the entire rectangular con- tainer from one-eighth of the original container. The coordinate (1,1,1) is the outermost corner, of the rectangle. Coordinate (NA,NB,NC) is the innermost corner (center of the container)'and NA.J.':UB and NC are the largest values of the spatial coordinates. Each grid point specifies a unique location within the rectangular container and has three values 25 which define that point. Within the computer program there are three arrays which correspond to the grid network. Each grid point or the corresponding descriptor has a temperature value, a bacteria.quantity, and nutrient 1ev31.which are internalized for all locations and change during processing. Using the finite difference approach to solve the problem, the time is first increased by one unit. In order to find the temperature at descriptor (1,1,1) the retort temperature is checked, (three sides of this grid location face the retort medium) second the three internal sides are checked. Figure 4.2 shows the relationship between one grid location and the six surrounding locations. The temperature of the sur- rounding volume influences the temperature of the center location. A weighted average is used in determining the center temperature and a similar procedure is followed for the other grid points. If the grid was not uniformly spaced, each of the sides would be a different size and carry a different weighting. The weighting scheme is built into the model. After descriptor (1,1,1) is determined the temperature value of (1,1,2) is calculated. This process continues until descriptor (NA,NB, NC) has been determined at which point the processing time is checked. The time is increased by one unit and the cycle is repeated until the program is completed. At this point, it is appropriate to discuss several terms which apply to the computer models. The terms are come-up time, heating time, decimal reduction or F8 value, cooling time, and percent retention. 1. Come-up time is the period of time required for the retort to reach the desired processing temperature (121° C). This process is energy intensive because steam is used to flush the air out of the re- tort. The come-up time is assumed to be constant for equal volumes of product. 26 A0 ,/’ /,/( 1/// V x -l/IQ/f 7' y (1.1,!) V2 FIGURE 4.1 Labeling of nodes for a rectangular parallelpiped for use in the computer simulation model. 27 / \ /, 4 FIGURE 4.2 A view of a central cube with surrounding locations. 28 2. Heating time is the total time period that the steam is required. For the same amount of time and equal product the energy utilization is constant. The retort temperature during this phase is 121° C. 3. Decimal reduction (D) and FS value are time and temperature relationships based on equation [5] which corresponds to a 90 percent reduction in the bacteria level. The decimal reduction is the time period required at a specified temperature to achieve 90 percent destruc- tion of an organism. The F8 value is a measure of the magnitude of the process and provides a convenient number to gage the reduction of bac- teria. If 90 percent of the bacteria are destroyed the PS value will equal 1.0. Should 99.9 percent of the bacteria be destroyed the FS value will equal 3.0. If the initial bacteria population.was 100,000 spores per standard size container and a final population (after heating) of 8210- 5 bacteria per container is used as the cut-off value to stop the heating process. In order to yield an F3 value of approximately‘ 10.0 with the overprocessing (kill greater than 81110.“5 bacteria per container) during the cooling phase. ‘The extra kill may be counted as a safety measure. 4. Cooling time is the time period required to cool the slowest heating point to an acceptable level (77° C). The cooling phase requires little energy, cool water, and time. The bacterial destruction which takes place during the cooling phase can be discounted or ignored de- pending on the method. The retort temperature during the cooling phase is 26' C. 5. Percent retention is the percent of the nutrient left after the processing has finished. The initial level is 100 percent. The percent difference between 70 and 65 percent, by convention, is 5 percent 29 of the original value. The modelled nutrient has the same decimal reduction and thermal destruction constant as thiamine (Hanson et.al, 1970). Thiamine is heat stable vitamin found in food products (Clifcorn, 1948). g The computer models have three criteria for termination which are process time completed, sufficient lethal kill, or instability of the model. The stability criteria is discussed later. Completion of the scheduled process time is normally used to terminate the models. This assumes that the desired process time is known and that the FS value is the desired output. The PS value would then be compared to company standards and the process time would be adjusted accordingly. Normally, the data would be compared with experimentally determined values. Sufficient lethal kill or desired number of bacteria is another method of determining process time. The assumptions are the same as the completion of the scheduled process time method. The value specified for sufficient lethal kill will determine the heating time required to reach the desired bacterial level. The sufficient lethal kill approach was taken in this study. Although, this method used an arbitrary bacteria kill, the approach provides useful information because heating time, cooling time, and the severity of the over-processing are all available for analysis. The ES value would be less than 10.0 if the product instantly cooled when the heating time was completed. As the FS value increases the lag time is lower or response time of the container is slower, and the quality decreases. .The sufficient lethal kill method is useful in quan- tifying differences between various sizes and shapes of containers. \ 30 4.3 Model Adoption and Verification Several changes were necessary to adapt each of the computer models discussed in section 4.2 to the sufficient lethal kill method. In order to adapt the rectangular model (Manson et.al. 1970) to the Michigan State University computer (Controlled Data Corporation Model 6500) changes were necessary because of undefined operand errors due to in— appropriate dimension sizes and parameters. The program was also con- verted from natural log to the base ten log because the food industry has traditionally used base ten in calculating the thermal destruction of bacteria. The original program.contained no explanation or comment statements. The revised program contains a variable list and comment statements. Computer simulation models need to be validated against actual situations in order to be of value. The models are adapted from pub- lished research so it is not necessary to repeat the original work of data collection. However, it is important to match the published values for each model and to compare these against other values found in literature. Manson et.al. (1970) did not clearly state thenmanner of validation he considered for the rectangular model. He did quote both Stumbo (1965) and Ball et.al. (1957) in discussing his results. Table 4.1 shows the comparison between Manson and the revised pouch model used in this study. There is a difference of 0.5 percent between the two models. Manson's model uses a combination of base ten and base e and the rounding error involved in the conversion accounts for the discrepancy. The pouch model has a built in stability criteria which is~based on the size of the container, the corresponding size increment, and the 31 time increment. The general stability equation for a onendimensional forward difference system is (Holman, 1976) $3523.- 2 [321 am: This equation can be rearranged to yield ZuAt ° ' 1 ‘ (Ax)2 - [331 Expanding equation [33] for three dimensions results in _2oAt - 2oAt - 2uAt” (AX)2 (Ay)2 (Az)2 O = 1 [34] Equation [34] was programmed into the rectangular model. The pouch model is unstable when the time increment is 0.4 minutes with the largest space increment equal to 1.8 cm. The number of space ins crements was not changed from Manson's model and the time increment was raised to 0.2 minutes. The cylindrical model (Teixeira et.al. 1969) required major modi- fications. Several important statements were missing and comment statements occasionally were faulty. The line continuation makers were not placed in column 6 and were inconsistent. Several statements were invalid and needlessly repeated. In general, the program used unneces- sary steps and tended to make things more complicated. One example is the repeated use of three level (positive, zero, negative) IF State- ments, when a simple (greater than) IF Statement would be sufficient. Lines with statement labels 8 and 9 in Teixeira et.al. (1969) are given as examples of inappropriate statements. The can model was mod- idified in order to perform bacteria and quality determinations during one program execution. A partial stability criteria based on equation [33] was also added. As published the model will not run, it is 32 TABLE 4,1 The validation of rectangular model comparing the original model to the revised'model. ' Percent Retention FS value Manson 68.04 9.18 Orlowski (Revised Manson 67.66 9.12 Model) TABLE 4.2 The validation of cylindrical model comparing Problem 2 in Teixeira et.al. (1969) and the revised model. Percent Retention FS value Stumbo —-- 5.45 Manson/Zebradnik -- 5.28 Teixeira (10X10)** 46.0* 5.34 Teixeira (5x5)** -- 5.06 0rlowski (Revised Teixeira 45.0* 5.22 model) *Based on DN ' 188 minutes ZN - 25 C° DN - decimal reduction time of the thiamine, the time at a specified temperature necessary to destroy 90 percent of the nutrient (minutes at 120° C) ZN - thermal destruction constant for thiamine (C°) ** Number of spatial increments 33 assumed that a rough draft of the model was published, In order to validate the corrections made in the model, problem number 2 in Teixeira et.al. (1969) was considered. Teixeira validated his model against Manson and Zahradrik and Stumbo as referenced by Teixeira et.al. (1969). The results of the current study (Table 4.2) fall within the accepted range. 1 i The numerical stability of the can model is most sensitive to changes in the time increment. When the time increment is large (0.20 minutes with a radial increment (Ar) of 0.44 cm and a height increment (Ay) of 1.16 cm) the system becomes unstable and unacceptable oscillation occurs. The exact level of instability was not determined. The time increment used in the can model is the same as that used by Teixeira, 0.125 minutes with a 0.51 cm radial and 0.43 cm height increment for the 5.08 cm radius and 8.57 cm.height can. Manetsch (1977) and Karleker et.al. (1977) discuss the importance of the time interval in relation to the stability of the model. 4.4 Comparison of the Can and Pouch Models A comparison between the pouch and can models provided the neces- sary linkage between the models. The comparison is based on extreme rectangular and cylindrical shapes. Table 4.3 contains a listing of the various size pouches and cans used to compare the two models. (Appendix C contains the complete computer print—outs of selected sizes.) As the rectangular shape is changed from a pouch to a cube the thiamine retention is reduced by 4.2 percent. The same trend is noticed for cylindrical containers changed from a shaft to a squat can. The rectangular shape can be made thinner or more compact than the cylindrical shape, simply as a matter of geometry (with a constant volume and reasonable dimensions). 34 The values are consistent between the two models. The pouch has better retention and the cube poorer retention than the squat can. Correspond- ingly, the longer and thinner cylindrical shaft has better retention than the shorter and thicker square shaft. Without the positive com- parison betweenwmodels-there would be no purpose in comparing further results. A summary of the various can and pouch sizes which were simulated is listed in Tables 4.4 and 4.5. Regular pouches are considered to be those which have a volume equal to 694.5 cm3 and the small pouches are those which have a reduced volume equal to 486.2 cm3. A square pouch has equal length and width and a rectangular pouch has a length three times the width. The container sizes considered ranged between 35.0 and 1.3 cm for any side, height, or radius. This variation allowed for a comparison between a wide spectrum of container sizes. The stability criteria of the models inhibited extreme dimensional changes. 35 TABLE 4.3 Comparison between models using extreme container sizes and a constant volume of 694,5 cm? ghgpg' Dimensions FS value 'Percent Thiamine Retention Pouch 1.90x19.112 , 9.91 69.95 Cube 8.863 10.98 65.72 Square Shaft 26.90x5.082 10.49 67.49 Squat Can 5.03xs.57** 10.42 66.53 Cylindrical- Shaft 2.54X34.26** 9.97 68.65 ** radius by height 36 TABLE 4.4 Dimensions of the container simulated by the retort pouch processing model* Thickness Length Width Type (cu) (CH!) (C!!!) 1.90 19.12 19.12 Square 1.90 11.04 33.11 Rectangular 2.54 16.54 16.54 Square 2.54 9.55 28.64 Rectangular 3.17 14.80 14.80 Square 3.171 8.55 25.64 Rectangular 3.81 13.50 13.50 ,Square 3.81 7.79 23.38 Rectangular 5.08 11.69 11.69 Square 5.08 6.75 20.25 Rectangular 8.86 8.86 8.86 Cube 26.90 5.08 5.08 Square Shaft 1.33 19.12 19.12 + Square 1.33 11.04 33.11 '+ Rectangular 1.78 16.54 16.54 + Square 1.78 9.55 28.54 + Rectangular 2.22 14.80 14.80 + Square 2.22 8.55 25.64 4+ Rectangular 2.67 13.50 13.50 4+ Square 2.67 7.79 23.38 + Rectangular 3.56 11.69 11.69 + Square 3.56 6.75 20.25 '+ Rectangular 7.86 7.86 7.86 + cube * Each container has the same volume (694.5 cm?), unless noted by a (+). + These containers have a volume of (486.2 cmd). TABLE 4.5 Dimensions of the'containsrs simulated by the can processing mode1.* Radius (cm) 2.54 2.94 3.17 3.50 3.81 4.37 5.08 5.38 5.89 6.35 6.60 7.61 37 Height (cm) 34.26 25.58 22.00 18.05 15.23 11.58 8.57 7.64 6.37 5.48 5.07 3.81 * Each container has the same volume (694.5 cm3) V RESULTS 5.1 Pouch Simulation Results The simulation results for regular (694.5 em3) and small pouch (486.2 cm?) are given in Table 5.1 The regular size pouches had re- tention values between 69.95 and 65.72 percent which correspond to 1.90 cm thickness (thinnest pouch) and a cube with each side being' 8.86 cm in length. The PS value varied from 9.91 for the thinnest pouch to 10.98 for the cube. The relationship between FS value and total time is consistent being 40.40 and 45.80 minutes for the thinnest pouch and the cube, respectively. The thinner pouch is expected to have reduced process time and improved quality, which is confirmed by the model. Increasing the pouch thickness while maintaining a constant volume will increase the process time (Figure 5.1) and the bacterial kill during the cooling phase with the same volume. The increase in pouch thickness will also cause a decrease in the percent retention of nutrients (Figure 5.2) The process time can be reduced 2.2 minutes and the nutrient retention improved by 3.8upercent byzusing a 1.90remethick.square4pouch.in place of a 5.08 cm thick square pouch. 5.2 Comparison of Square and Rectangular Pouches The reason for comparing square and rectangular pouches is the fact that pouches are basically confined to these shapes. The differ- ence in processing time between a square pouch and a rectangular pouch 38 39 37.60 POUCH SIMUALRTION MOiDEL 3:7.”0 Square Pouch 35.80 Rectangular Pouch .40 36 36.00 Pouch Volume - 694.5 cm3 HEATING TIME (MINNES) .5 0 35 L, 5.20 '3 .00 4500 6.00 01.00 70.00 THICKNESS .(cm) NJ 0.00 FIGURE 5.1 Variation in heating time with thickness for a conduction heating food in square and rectangular pouches. THIAMINE RETENTION (Z) 7fla40 .00 83-80 69.50 67.20 68 .40 56 1 40 POUCH SIMULRTION MODEL Square Pouch Pouch Volume - 694.5 cm? Rectangular Pouch c{55.50 I‘d O C) 4300 sioo 8.00 10.00 THICKNESS (cm) FIGURE 5.2 Variation in the percent retention of Thiamine with thick, ness for a conduction heating food in square and rectangular pouches. amao m.¢mo ea oasao> ecu engsuocuov ossHo> mac ~.cme :uus raccoon + Amcuaoou usuvsuocqv mafia mmoooum ouuusm «ea co locum Aug: He>ueucq mafia ‘K II mososoa weusmmsuoou was Quasar ou women a are m I! 41 cc.nv cm.hm ~m.o~ mm.nc nca.c mn=U+ mm.n cq.~¢ cc.cn -.cn on.~o mmm.¢ ¢+ cm.n cc.~c cc.on am.a an.no Nom.c m+ on.n co.H¢ oo.om am.a oe.mo enm.o ¢+ sc.~ c~.Hc om.mm hw.a no.ao mem.c m+ so.~ oo.~q cc.mm m~.a mo.ac mNH.H a+ -.N oc.c¢ oe.nn em.¢ nn.ab sac.~ m+ ~N.~ c¢.c< o~.mm e~.a Hm.me eh~.~ a+ w~.a c~.o< cc.nm n~.a co.c~ omn.~ m+ m~.w c~.oe co.mm h~.m Hm.c~ NmH.a m+ ~m.~ o~.ce cc.mm qu.m mn.oh «No.~ m+ ~n.~ c~.mq oc.em we.c~ me.~o Nun.o Hha>usm «essence «eucqueoz os~a> mm ucoouom no “04332 «ache mmocxouce .cosoe a sq vengeance coon nausea: cofiuosecou mo maauaeooue Heeuocu ecu acqucassam no auasmom H.m manda 42. with the same thickness and constant volume was small. For example when the pouch.thickness is 3.17 cm the heating time is the same (36.20.minm utea) for both a rectangular and a square pouch (Figure 5.1). A square pouch can.be processed slightly faster than a rectangular pouch when thickness is less than 3.17 cm. The reverse is true for thicknesses greater than 3.17 ems A 5.08 cm thick rectangular pouch requires 0.6 minutes less heating time than the corresponding pouch. Similar results were obtained with respect to nutrient retention. .5.3 Can Simulation Results The can model indicates (Table 5.2) the least process time (46.63 minutes) and the best nutrient retention (68.65 percent) occurs with a 2.54 cm radius and 34.26 cm height can, which is.the limiting height. The greatest bacterial kill (F3 value of 10.42), longest process time (49.63 minutes), and the least nutrient retention (66.53 percent) occur with the 5.08 cm radius and 8.57 cm height can. The relationship of the heating time required for cans based on the radius is shown by Figure 5.3. Changing the diameter with constant volume has a greater effect than changing the height. The geometry of a 2.54 cm.radius can has 360° of heat transfer surface 2.54 cm.from the cold spot. A 5.08 cm tall can has only 2 surface points that are 2.54 cm.from the slowest heating point. By comparison the 5.08 cm.diameter can has a heating time 0.9 minutes less than the 5.08 mm tall can. Changes in the can radius have little effect on the nutrient retention (Figure 5.4), only a 2.5 percent change over the simulated range. 5.4 Comparison Between the Pouch and Can Simulation Studies The energy difference between heating cans and pouches of the same 43 chqaoou mswvsaoswv mafia mmoooua unseen «as .so Boone ecu cow: ~e>wousw «Bus «e » »L .;,-,r. - :L L.Lmnnw>usm «essence «ensues»: m=~a> we penance no nuaasz news»: assume .msoo ca oasqeusoo meow mayhem: coquosocoo mo msammoooua assuage on» mowuedsaam mo cadence ems ~.m ugm case one o>oc mnooweuooo Mac «I coo. ama.c Iamn ~¢.n h.mmm can ca.c~ III: amfi.c .can ce.¢ n.a~< mmbu em.m dam. an~.c Numn mm.¢ a.s¢m M ac.m mac. mnH.c .cmn ~o.e m.c~n m mo.m mac. mnH.c .qmn c¢.n n.~co a mm.m new. cma.c .Nmm oa.m H.Hnn m mm.m «no. and.c .cmm Hm.n c.cno m «H.m omn. mmH.c .oan oc.m w.c~o m mH.m Nun. mn~.e .cmn ch.o n.~¢~ M cm.~ new. mnH.c .mmm oe.o um.q~s . m cm.~ «ha. snd.c .amm HH.¢ H.maa m ca.n mom. mma.c .mmm um.h «.mmm m ca.~ 3 30:33 3: arouses: socioecoo woe oo>oueaw on umoo congress on umoo Ausov Aaov «0 once ransom amuocu finances: sou< waxy eaomoexowca .ooufie esoquo> mo essence uo moqomoooue assuage one wouueaosau an ooueasoaso somfiuoeeoo umoo was >muocm m.m uqm ease as» o>o= euocueuooo ~H< e aIIIII IIIII .qan ~.oa ~.hem Ho.~ sam.~ mmu.c .eam e.e~ m.eme cc.c oan.n mmu.o .ean ~.o~ n.-e mm.o mac.n mm~.c .emm «.ma «.mme ma.m ccm.s am~.c .emm c.nu c.oe¢ mm.m IIIII ann.c .emn a.<~ «.mne mo.n ccc.~ am~.c .cmm c.ma m.nm¢ sm.¢ cm~.~ mm~.c .emn o.m~ c.cm¢ Hm.n sme.a mmu.c .mmn m.c~ c.c~¢ om.e eoe.~ mmn.o .Nmm ~.~H o.ccm sa.m nu~.~ ama.c .Nmm m.hu m.¢~m oa.~ mev.~ mn~.o .Hmm H.c~ c.5mn on.~ 2.5 on cowuoouou nocueuooo «we accuses: oe>ouaeu on ueoo penance» on umoo annoy Aaov no uooo >muoou zmuocu finances: sou< asavsm .eouue coo osouus> no woweeooona Hosanna ecu mogueasswe he oouensoaso someonesoo uses one hmuoom e.m mam ease was e>sn unmeasuooo ~H< a III... .236 63 an...“ as: $8 3 .e cm~.c .hao.o .cds sn.m ~.~Aq m om.m Hm¢.c .hac.c .sus no.n «.anc m om.n ~mn.¢ .emc.c .mas cm.¢ s.omm a no.~ Hos.¢ nomc.c .nae cc.¢ m.ocn m no.~ aao.c cmc.o .Nas ~m.m m.mmm 1 -.~ aum.c oec.c .mus ma.m m.sem m -.~ adm.c omc.c .Nue -.o ~.nmo m m~.~ cec.c cmc.c .Has oc.w e.nnc m m~.~ cam.o Jcacd .Hue so.n n.m¢m m ~m.~ aso.o .oac.c .dae on.“ n.a~a m ~n.a _, . 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NNudmuhbhhhhhhhhh H2 HMZZZZZZZZZZZ 0¢NH nunnmunnmnn 0h 2(200030000000 0 OZ~°¢¢mmamaammm 000 10 maoouoooooooooooc NOGdP 33343333334 ":0 0 00000000000' OFNH‘NUUUUUUUQUUU panama "22 uuuuuuuuuuu‘ cub anzzxzzzzzzz Oh OOWFFPthhthh 0 Go a d6h0¢0hbhhhhhhhhh anew <2<<<¢¢<<<< 0th . ummnauuuuuuuuuuuu: .ocnnaczmmmmxmzzxz a nu; 33332223223' uzu hhhhbhhhhbh‘ caohon<<<<<¢<<<0” >P0 22m 3“ WP m" 22 O m P3 223 UM‘ 2U) 22‘ :um 2&2 APPENDIX D Energy Cost Equations 70‘ ENERGY’ COST EQUATIONS Natural Gas .25135¢/£t3 g... (COnamner‘s Power Michigan September 1979) Efficiencies 0.92 of heat exchanger (Balm, 1976) 995.4 BTU/ its gas (Henderson and Perry, 1976) 1087.9 BTU/ lbm steam (Reynolds and Perkins, 1977) -l BTU - 1.055 It)" 42 cases of 24 number two cans require 420 lbm steam for the first 15 minutes, after 15 minutes 125 lbn steam per hour of heating time (Lopez, 1975). Energy Required for 30 minutes (420 lbs steam/retort) + (125 lb steam / hr retort)‘.*(15 min) = 450.0 lbs steam/retort ' far each additional minute (125 1b steam/60 min retort) - 2.08 lb steam/min retort example a 1.90 cm x 19.09 cm x 19.09 cm pouch has a heating time of 35.2 minutes 1.055kJ 1087.9 am ’450 lbs steam 2.08 lb steam I) - + O ( 1 BTU )( 1b steam X retort additional minute-retort x 5 2 - (42 casefretort) x (24 pouchesfcase) x (.92 efficiencies) kJ pouch - 588 cost per pouch u " 1 3m '\ £t3 V1513“) 0.1379 (588 pouch)(1.055 Ind/995.4 ‘n‘m ' £t3 " pouch 71 cost for small pouch (702 of the volume or the regular pouches) 1.32 cm x 19.09 cm x 19.09 cm withj‘heat’ tine of 35.00 minutes .. .7 regulva'rfpouch; 1.05; gm “mafia-rm“) 450 +~ 2.08 x 5.0‘lba'ste'am- small pouch / BTU .. "If: 'steau' ' ' . retort w w— 2 2 (42 case/retort) x (24 pouChes/case) x (.92 efficiencies) 2 k3 411 ' small pouch cost per small pouch '411. 1a» \ 1, 31g 1:3 X13135; _ 0.096¢ small pouch} ' 1.055 kJ' 995.4 BTU ft small pouch LIST 0? REFERENCES LIST 0? REFERENCES Abbott,.R.C. 19771 The Retort Pouch.From Concept To Reality In the American.Market. The Packing institute, St. Louis, Missouri. April 21, Andres, C. 1979. Retort Pouch Research Efforts Shift to Food Formula— tions, Food Processing 40 (9)344—46. Ball, C.O. and F.C. Olson. 1957. Sterilieatign in Feud Technslggz,‘McGraw— Hill, New'York. Banner, R. 1979; What's Next For The Retort Pouch? Food Engineering 51(4): 69-75. Board, P.W} and R.J. Steel. 1978 Calculating Heat Sterilization Processes for Canned Foods.‘ Food Technology~in AustraliaJMay: 169n173.) Clifcorn, L.E. 1948. Factors Influencing Vitamin Content of Canned Foods. Advances in Food Research 40: 84-89. Davis, R.B., qu. Robertson and F.E. Long. 1972. Engineering Considera- tions in Retort Processing of Flexible Packaging. Food Technology 26(8):65—8. Donley, J. 1979, July. Nu Foods Edmore Michigan. Personal Communications. Europe's First Automatic Retort Pouch Line Now*in Action, 1979. Food Processing Industry 48(568):60-63. Foster, F. 1979, May. Michigan Canners Association, Benton Harbor, Michigan. Personal Communication. Goldfarb, P.L. 1971. Pouch For Low~Acid Foods 1:. Modern Packaging 43(12):70-76. Goldfarb. P.L. 1971. Pouch For Low-Acid Foods II. Modern Packaging 43(1):70-76. Henderson, S.M. and RcL. Perry. 1976. .Agricultural Process Engineering. AFT. weatport. Herndon, D.H., R.C. Griffin, and 0.0. Ball. 1968. Use of Computer Derived Tables To Calculate Sterilizing Processes For Packaged Foods. Food Technology 22(4): 129-239. 23(4):121. 25(2)3134—l43. Holman, J.P. 1976. Heat Transfer. MbGrawvHill, Inc., New~York. Karlekar, B.V. and RWM. Desmond. 1977. Engineering Heat Transfer. West Publishing Company, New York. Lampi, R.A., G.L. Schultz, T. Ciavarini, and P.T. Burke. 1976. Pre- ' formance and Integrity of Retort Pouch Seals. Food Technology 30 (2):38—48. Lemaire, W. 1978. The Retort Pouch - Where we Now-Stand. Food Engin- _ eering 50(8):61-64. 72 73 Lustucru‘s New'Retortable Pouch Line, 1979.. Food Engineering-51(4);76—78. ‘Msnetsch,‘T.J. and G.L. Park.’ 1977. System Analysis and Simulation.with Applications to Economic and Social Systems, Part II. Department of Electrical Engineering and System Science. 'Michigan State Uni— versity, East Lanaing,‘Michigan. Manson, J.E. and 3.“: Zahradnic. 1967. Computer Thermal Process Determin- ation for Conductions-Heated‘Foods.~ Food Technology 21(9):42—46. Manson, J.E., C.R. Stumbo, and J.w; Zahradnic. 1974. Evaluation of Ther- mal Processes for Conduction Heating Foods in Pear Shaped Containers. Journal of Food Science 39:276—282. Pereira, V.P. 1978. Processin of Green;Beans ianetortable Pouches. Unpublished M.S. Thesis, Department of Food Science,‘Michigan ' State University, East Lansing,‘Michigan. Pflug, I.J., H.J. Bock and F.E. Long. 1963. Sterilization of Food in Flexible Packages. Food Technology l7(9):87-92. Pflug, I.J. and C. Borrero. 1965. Evaluation of the Heating Media for Processing Shelf Stable Foods in Flexible Packages in Commercial Processing Equipment. Unpublished work, Department of Food Science, Michigan State University, East Lansing, Michigan. Pinto, A. 1978. Retort Pouch: Moving to Close the Materials and Machinery Gap. Modern Packaging 50(4):23:28. Reynolds, R.C. and H.C. Perkins. 1977. Engineering Thermodynamics. McCraw- Hill, New York. Rubinste, F.S. 1964. Army's "Obstacle Courses" Yield a New Look in Food Packaging. Food Technology 18(11): 73-74. Schulz, G.L. 1978. Trends in Food Packaging for Food Service. Journal of Food Protection 41(6):464-467. Stumbo, C.R. 1965. Thermobacteriology in Food Processing, Academic Press, New York. Teixeira, A.A., J.R. Dixon, J.W. Zahradnik, and G.B. Zinsmeister. 1969. Computer Optimization of Nutrient Retention in the Thermal Proces- sing of Conduction Heated Foods. Food Technology 23:845-850. Teixeira, A.A. 1978. Conduction-Heating Considerations in Thermal Processing of Canned Foods. 78—WA/HT-55. 'Winter Annual Meeting, San Francisco, California, December 10-15. Thomas, G.B. 1969. Calculus and Analytical Geometry. Addison-Nealey Publishing Company, Reading, Maryland. User of Retort Pouch Adds Higher-Speed Line. 1979. Food and Drug Packaging, March 22, 40(6). - 74- Wilson, D.C. 1970. Congruous Processing of Flexible Packages. Innovation in Food Engineering. Santa Clara, California. March 23. General Bibliography Addinall, C.R. 1940. T59-SP9r?-°§-V$E§E§n.Pl' Merck and Co. Rahway, New~Jersey. . Alstrand, D.V. and Ecklund. 1952. The Mechanics and Interpretation of Heat Penetration Tests in Canned Foods. Food Technology 4(5):185-189. Arpaci, v.3. 1966. Conduction Heat Transfer. Addisonrwesley Publishing Company, Reading, Massachusetts. Ashover, E. 1976. Retort Pouch Line is Fully AutomaticéModular Concept Metapak. Packaging News 4:1,30,44. Ayoub, J.A. 1974. Continuous Microwave Sterilizing of Meat in Flexible Pouches-Equipment. Journal of Food Science 39(3):309—13. Berry, M.R. 1979. Retort Pouch: Critical Processing Parameters. Food Engineering 51(6):94-95. Bobanza, L.L. 1977. Uncle Same wants Ybu to Package Products In the Re- tort Pouch. Food Engineering 49(11):58-61. Brody, A.L. 1971. Food Canning in Rigid and Flexible Packages—Retort Equipment, Thermal Processing Equipment. Food Technology 25(7): 187-243. Brody, A.L. 1971. Aseptic Packaging of Foods. Food Technology 26(8):?0—74. Buric, A.C. 1974. Retortable Flexible Food Packaging Market and Economic Analysis- Semi-Rigid Trays, Convenience Foods, Energy Conservation, Japan, Europe, Costs Production Lines. Annual National Packaging Forum of Packaging Institute, Chicago. October 7-9. Burke, P.T. and G.L. Schultz. 1972. The Comparative Performance of Flexible Packages and Metal Cans. Technical Report 73-62 U.P. U.S. Army Natic Laboratories, Natick, Massachusetts. Calculation of Processes for Canned Foods. 1964. American Can Company. Maywood, Illinois. Carslaw, H.S. and J.C. Jaeger. 1978. Conduction of Heat in Solids. OXv ford University Press, Great Britain. Chapman, 5. and B.J. McKernan. 1963. Heat Conduction into Plastic Food Containers. Food Technology 17(9):79-82. 75 761 . Davis, E.G.,'M. Karel, and B.E. Proctor. 1960. The Pressure VOlume Re1a« tion in Film Packages during Heat-Processing. Food Technology 14(3): 165-169. 1 Davis, RNB. and D.T. Maunder. 1967. New*3ystem for Asceptic Pouch Pack- aging Sterile Filling and Sealing, Microbiological Studies, UV Ra- diation, Superheated Steam Sterilization. Modern Packaging 40(10): 157—163. Densford, L. 1979. Army Set to Buy Retort Pouch for Rations. Food and Drug Packaging 40(3):16. Dickerson, mex 1969. Simplified Equations for Calculating Lethality of the Heating and Cooling Phases of Thermal Interaction Determinations. Food Technology 23:108-111. Duffy, P.J. 1973, Aseptic Filling in Flexible Bags. Food Technology 27(9):52. Duxbury, D.D., P.F. Same, WkF. Howeler, J.A. Gee, and was. Muller. 1970. Reliability of Flexible Packaging for thermoprocessed Foods Under Production Conditions, Phase I Feasibility. Technical Report 72-77 G.F. U.S. Army Natick Laboratories, Natick, Massachusetts. Europe‘s First "high speed" Pouches. 1979. Food.Manufacture"54(2):45—47. Feliciotti, E. and W33. Esselen. 1956. Thermal Destruction Rates of This— ’ ‘mine in Pureed Meets and Vegetables. Food Res. 11(2). Goldlith, S.A., M.A. Jodlyn aner.T.R. Nickerson. 1961. Introduction To The Thermal Processing Of Foods. AVI, weaport. Hayakawa, K. and 6.0. Ball. 1968. A Note on Theoretical Heating Curve of a Cylindircal Can of Thermally Conductive Food. 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Kenyon, EJM., D.B. westcott, andTJ.W\ Gould. 1971. 7A System For Contina uous Thermal Processing of Food Pouches Using’Microwave.Energy. Journal of Food Science 36:289n93. Laboratory Manual for Food Canners and Processors. Volume 2, 1968. AVI. westport. Lampi, R.A. 1974. The Reliability Programm Meeting—inéMinature New York Institute of Food Technologists.. January 15. Lampi, R.A. 1977. Flexible Packaging for Thermoprocessed Foods. Advances in Food Research 22:304-377. Langewis, C. 1979. Reducing the Cost of Drawn and Ironed Cans. Food Engineering 51(4):88—89. Lawrence, C.A. and 3.8. Block. 1968. Disinfection, Sterilization and Preservation. Lea and Febiger, Philadelphia. Leading Retort Pouch Processor Plans Expanded Output. 1979. Food Product Development 13(4):46. Lenz, MLK. and D.B. Lund. 1977. The Lethality-Fourier Number Method Exper— imental Verification of a Model for Calculating Temperature Profiles and Lethality in Conduction Heating Canned Foods. Journal of Food Science 42(4): 989-1007. Lemaire, W. 1977. we need Innovation . . . This Is It. Food Engineering 49(11):52-56. Lillquist, R.A. 1979. The Super Markets For Flexible Packaging. Paper, Film, and Foil Converter 53(3):33-36. ' Lopez, A. 1975. A Complete Course in Canning. 10th Edition Volume I and II. The Canning Trade, Baltimore, Maryland. Manson, J.E., J.W. Jahradnik, and C.R. Stumbo. 1970. Evaluation of Leth- ality and Nutrient Retentions of ConductionrHeating Foods in Rectane gular Containers. Food Technology 24(11):109-113. Mermelatein, N.H. 1976. An Overview'of the Retort Pouch in the U.S. Food Technology 30(2):28-37. Myers, G.B. 1971. Analyticaleethods in Conduction Heat Transfer. McCraw—Hill, New‘York. Navankasattusas, S. and D.B. Zund- 1978. Monitoring and Controlling Thermal Processes by On—Line Measurement of Accomplished Lethality. Institute of Food Technologists 4: 79—83. 78‘ Nelson, A.I., and MRP. Steinberg. 1956. Retorting Foods in Plastic Bags. Food Engineering 28(1):92—93. ‘ Non-Rigid Containers. 1975.- Canner/Packer 144(3):60v61. Olson, F.C. and JgM. Jackson. 1940.. Heating Curves, Theory and Practice. Industrial Engineering Chemistry. 34:337. Ordway, G.B. and G.L. Schultr.’ 1972. Inspects Package Seals. Food Engineering 44(2):64-65. Peters, J.W\ 1975. Retail Debut of Retort Pouch Earns Consumer Accep- tance Of Food Packing. Food Product Development 9(2):22«31. Pflug, I.J. 1964. Evolution of Heating Media for Producing: Shelf Stable Foods in Flexible Packages.Phase I. Final Rep. Contract DAI9nAMC—I45 (N) Natick, Massachusetts. Rubinste, F.S. 1973. Thermoprocessed Foods in Flexible Packages: Tran- sition to Production. Package Development July: 12-29. Scheider, P.J. 1957. Conduction Heat Transfer. Addisonrwesley Publishing Company,‘Massachusetts. Seligsohn, M. 1977. .Alturnate Pouch Zips by FDA, USDA, as Food Firms EIE its Potential. Food Engineering 49(7): 20—25. Semling, B.V. 1979. 1979 Packaging Forecast. Food Processing 40(3):56-59. Tung, M.A. 1975 Quality Comparison of Cream Style Corn Processed in Rigid and Flexible Containers. Canadian Institute of Food Science and Technology Journal 8(10): 211-216. Tung,‘M.A., MkP. Garland, A.R. Maurer. 1977. High Quality, Heat Processed Vegetable Products Prepared in Flexible Pouches. Food Product Development 11(7): 1125121. '